Hang-free thread design

ABSTRACT

A threaded pin and box connection having thread geometries and/or dissimilar thread fits that prevent the pin thread of a connection from hanging up in the box thread as the pin is being stabbed into or destabbed from the box. Dissimilar geometries and/or threads include dissimilar thread types, dissimilar leads, overlapping leads, thread tooth widths of one component greater than thread grooves of the other component, multiple start threads, and combinations thereof.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to threaded connectionsused in securing two components together. More specifically, the presentinvention relates to a threaded pin and box connector for assemblingtubular pipe bodies to each other.

[0003] 2. Background Setting of the Invention

[0004] The pipe used in the construction of wells is usually in the formof a long tubular string assembled from a number of small pipe sections.The pipe can be used as a drill string, a casing or tubing string, atendon for offshore rig anchoring or other applications requiringconnection together of individual threaded components. The pipe sectionsare secured together at their ends by an externally threaded connector,or “pin” that is threadedly received within an internally threadedconnector or “box”. Each pipe section has a pin on one pipe end and abox at the opposite pipe end. Some pipe has an internally threadedcoupling secured to one end of a double pin pipe section to produce thebox. The individual pipe sections are frequently referred to as a “pipejoint”. Tubing and casing pipe joints are usually 30 ft. in length.Casing pipe joints typically vary in length from 20 ft. to 40 ft. orlonger.

[0005] The various pipe strings used in constructing a well are usuallyassembled on the floor of a drilling or workover rig. The pipe string islengthened and lowered into the well as succeeding pipe joints are addedto the string. During this assembly procedure, the pipe joint beingadded to the string is lowered, pin down, into an upwardly facing boxprojecting from the drilling rig floor. This procedure is commonlyreferred to as “stabbing” the pin into the box. After being stabbed, theadded pipe joint is rotated to engage the threads of the pin and box,securing the joint to the string.

[0006] In disassembling a string, the previously described process isreversed. The pipe joint at the top of the string is rotated todisengage the pin and box threads. Once the threads have disengaged, thepin is lifted out of the upwardly facing box projecting from the rigfloor. This procedure is sometimes referred to as “destabbing” the pinfrom the box. Once free of the box, the removed joint is moved to astorage location.

[0007] Thread damage can occur if the pin is not cleanly stabbed intothe box of the connection. If there is misalignment between the pin andbox as the joint is lowered into engagement with the box, the face andside of the pin can strike seals and threads in the box causing damageto both components of the connection. The use of a stabbing guide when ajoint is being added to the string minimizes stabbing damage. Thestabbing guide centralizes the pin over the box and prevents the pinfrom striking the box threads or seals as the pin is being stabbed intothe box.

[0008] A problem with disassembling certain threaded pipe strings isthat the pin and box threads can hang on each other when the pipe jointsare being destabbed after having been unthreaded from each other. Ahang-up of the pin and box threads during destabbing can seriouslydamage both components of the threaded connection and can also causeinadvertent release and dropping of the entire pipe string or injury topersonnel.

[0009] The probability of a hang-up is increased in multi-step threadforms where the threads are machined on adjoining cylindrical surfaceshaving dissimilar diameters. A multi-step thread design is beneficial inthat it permits a threaded pin to be stabbed deeply into a threaded boxwithout relative rotation between the two pipe joints. Once the pin isstabbed, threaded engagement of multi-step pin and box threads iseffected by a relatively few number of turns of the pin into the box. Bycontrast, full makeup of non-tapering single step connections requiresthat the pin and box threads be rotated relative to each other a numberof revolutions that equals the number of connection thread revolutions.

[0010] Certain two-step drill pipe connections currently used in priorart designs employ a two-step wedge thread. A two-step thread designthat employs a wedge thread is particularly susceptible to hang-upduring stabbing and destabbing of the connection. The increasedsusceptibility results from the fact that the wedge thread tooth changesin width over its length so that a relatively narrow pin thread can comeinto registry with relatively broad spacing between adjacent box threadteeth during stabbing and destabbing. If the centerline of the pin isdisplaced from the centerline of the box during the stabbing anddestabbing motion, the threads near the end of the pin will hang-up inthe threads near the face of the box. When the threads hang-up duringdestabbing, it is necessary to slightly lower the joint, center the pinwithin the box and then lift the pin free of the box. If large forcesare exerted on threads after they have hung up, serious damage may bedone to the threads of the pin and box.

[0011] The special care required to prevent hanging up of the threadswhen a drill string is being laid down or placed back in the derrick istime consuming and can unacceptably extend the time required to pull thedrill string from the well. The designers of the prior art wedge threaddrill pipe address the problem by providing a centralizing destabbingguide that can be placed over the connection before the unscrewed pin islifted out of the box. Proper placement of the destabbing guide aroundthe connection requires additional personnel effort and extends the timerequired to remove the pipe string from the well. Moreover, thecentralizing guide may not be effective in maintaining centralization ofthe pin and box under certain conditions such as occur, for example,when a strong side wind is present or when the drilling rig top drive orblock is not properly centered over the drill string box.

[0012] Constructing the thread diameters of two-step connections with aslarge a difference in diameters as possible reduces the probability ofthread hang-up during stabbing and destabbing. This design tacticpermits greater centerline displacement to occur between the pin and boxbefore the thread teeth on the side of the pin engage the thread teethon the inside of the box. However, in order to achieve this reduction inhang-up without weakening the connection, the external dimensions of theconnector must be increased and/or the internal passage through theconnector must be decreased. Good string design dictates that theexternal and internal diameters of a threaded connector be maintained asclosely as possible to the external and internal diameters,respectively, of the pipe bodies being secured together by theconnector. Extending the outside diameter of a connector or reducing theinternal clearance through the connector to minimize the incidence ofthread hang-up on stabbing or destabbing compromises optimum connectiondesign.

SUMMARY OF THE INVENTION

[0013] The present invention solves the problem of thread hang-up byproviding connection geometries such as thread forms, dimensions, and/ordissimilar thread fits that prevent lateral entry of the pin threadtooth into the gap formed between adjacent turns of the box thread toothduring all, or virtually all, times when the box threads overlap the pinthreads as the pin is being stabbed into, or destabbed from, the box.

[0014] In a preferred form of the Invention, the crest of the pin threadtooth at the end of the pin is larger than the width of the spacing, orthread groove, between adjacent turns of the box thread tooth at the endof the box. The wider dimension of the pin thread tooth prevents the pinthread tooth from entering the smaller dimension of the opening betweenadjacent turns of the box thread tooth.

[0015] In the design of the present invention, the smaller width pinthread tooth is never in radial registry with the larger width boxthread groove, which prevents the pin and box threads from hanging up ineach other. In prior art designs subject to hang-up, narrow pin threadteeth are in registry with the larger diameter box thread grooves duringthe stabbing and destabbing procedure.

[0016] The thread design of the present invention permits the use of amulti-step thread form without regard to problems associated with threadhang-up. As a result, all of the benefits of a multi-step connection canbe obtained without undesirably increasing the external dimensions ofthe connection or diminishing the connection strength.

[0017] The design of the invention provides additional safety in pipehandling by preventing accidental release and dropping of the stringinto the well following a hang up during removal of pipe sections fromthe string.

[0018] A multi-step thread form in a drill pipe connection, using thedesign of the present invention, enables the wall of the engagedconnection to be reduced significantly, which increases the flexibilityof the connection, reduces the incidence of fatigue failure in theconnection, provides a larger central internal diameter for fluidpassage through the connection and enables the formation of the threadson a reduced size upset at the end of the pipe.

[0019] The thread design of the present invention can be incorporated invirtually any thread form, including, but not limited to V, tapered,square, round, hooked, dovetail, wedge, Chevron, semi-dovetail, multifaceted and combinations of these thread forms.

[0020] A novel feature of the thread form of the present invention isthe provision of a multi-step pin thread in which the width of the crestof a helical pin thread tooth is greater in the threaded step adjacentthe end of the pin than it is in the step removed from the end of thepin.

[0021] In a modified form of the present invention applied to amulti-step wedge thread, the lead of the large step box thread is madeto differ from the lead of the small step pin thread so that the crestof the pin thread tooth spans the gap between the crest of adjacentturns of the box thread tooth during stabbing and destabbing, therebypreventing entry of the pin thread tooth into the groove or gap betweenadjacent turns of the mating box component. The load flank lead of thebox thread is made smaller than the load flank lead of the pin threadwhile the stab flank lead of the box thread is made greater than thestab flank lead of the pin thread. The average lead of the pin thread isthe same as the average lead of the box thread, enabling the connectionto be screwed together. The potential area for hang-up in a wedge threadwith dissimilar leads is limited to a small part of the total threadarea near the axial end of the pin connection and the face of the boxconnection.

[0022] The no-hang feature of the present invention enables theconstruction of a threaded connector on a pipe joint having a smallerupset than is required for the construction of a conventional connectorusing a similar thread. Significant cost savings may be effected in themanufacture of a, pipe string of the present invention because of thehigher costs associated with the fabrication of the larger pipe upsetsrequired for the construction of conventional connectors.

[0023] The ability to make the composite wall of a connector of thepresent invention thinner than that of a conventional connector usingthe same or equivalent threads increases the efficiency of fluidtransfer through the connection, contributes to a reduction in fatiguefailures of the connection, permits the use of a string using theconnector in more highly deviated wells, and enables fabrication of theconnector on a smaller pipe upset. All these features improve theperformance of the pipe string and contribute to a reduction in the costof manufacturing and using the pipe string.

[0024] From the foregoing, it may be appreciated that an importantobject of the present invention is to provide a thread construction thatprevents thread hang-up during stabbing or destabbing of a threadedconnection.

[0025] Another object of the present invention is to provide a threadconstruction for a multi-step thread connection in which the threaddiameters of the various threaded step areas may be made as close insize to each other as possible without regard to the probability ofthread hang-up.

[0026] An object of the present invention is to provide a threadconstruction that can be applied to a variety of different thread typesfor preventing thread hang-up during stabbing and destabbing ofconnections.

[0027] An object of the present invention is to provide a non-hangingthread construction that permits the construction of a drill pipe stringthat is more flexible than that of a similar drill pipe string withthreads that can hang-up during stabbing or destabbing.

[0028] It is also an object of the present invention to provide anon-hanging thread form that permits the construction of a string ofpipe with smaller connection dimensions than those of prior art pipestrings.

[0029] Yet another object of the present invention is to provide athread design in which the thread tooth width exceeds the box threadgroove width at every axial position where a pin thread and box threadare adjacent each other during stabbing or destabbing of the pin andbox.

[0030] Another object of the present invention is to provide amulti-step threaded connection in which threads in a first step adjacentthe free end of the connection have a width that is greater than thewidth of the threads on a second step further removed from theconnection end.

[0031] It is also an object of the present invention to provide matingpin and box thread forms that are dimensioned and positioned to causethe pin threads to span the grooves between adjacent turns of the boxthreads during stabbing and destabbing to thereby prevent hanging of thepin threads in the box thread grooves.

[0032] A specific object of the present invention is to provide a pinand box connection having wedge threads wherein the lead of the pinthreads and box threads are dissimilar while the average pin and boxthread leads are maintained equal to each other to thereby permit theconnection to be screwed together while simultaneously preventinghang-up during stabbing and destabbing.

[0033] The foregoing objects, features and advantages of the threaddesign and method of the present invention will be better understood andmore fully appreciated by reference to the following drawings,specification and Claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a vertical cross sectional view of an engaged pin andbox connection of the prior art having a semi-dovetail, wedge helixthread profile;

[0035]FIG. 2 is a vertical cross sectional view of the prior artconnection of FIG. 1 illustrated following disengagement of the threads,before destabbing the pin from the box;

[0036]FIG. 3 is a vertical cross sectional view of the prior artconnection of FIGS. 1 and 2 illustrated with the pin and box threadshanging up as the pin is being destabbed from the box;

[0037]FIG. 4 is a vertical cross sectional view of an engaged pin andbox connection of the present invention having a semi-dovetail wedgehelix thread profile;

[0038]FIG. 5 is a vertical cross sectional view of the pin and boxconnection of FIG. 4 following disengagement of the pin and box threads,before destabbing the pin from the box;

[0039]FIG. 6 is a vertical cross sectional view of the pin and boxconnection of FIGS. 4 and 5 illustrated with the pin and box threadsengaging without hanging up midway through the destabbing process;

[0040]FIG. 7 is a vertical cross sectional view of the pin and boxconnection of FIGS. 4, 5 and 6 illustrated with the pin and box threadsengaging without hanging up at the end of the destabbing process;

[0041]FIG. 8 is a vertical cross sectional view of a non-wedge, hookedthread pin connection of the present invention being destabbed from amating box connection without hanging up of the threads;

[0042]FIG. 9 is a vertical cross sectional view of a positive flankthread, non-wedge pin connection of the present invention beingdestabbed from a mating box connection without hanging up of thethreads;

[0043]FIG. 10 is a vertical cross sectional view of multi-faceted, dovetail wedge thread pin connection being destabbed from a box connectionwithout hanging up of the pin and box threads;

[0044]FIG. 11 is a vertical, quarter sectional view of a conventionaltwo-step connection constructed with large spacings between two adjacentthread steps to reduce the incidence of thread hang-up;

[0045]FIG. 12 is a vertical, quarter sectional view of a 2-stepconnection such as illustrated in FIG. 11 constructed in accordance withthe teachings of the present invention;

[0046]FIG. 13 is a an enlarged schematic representation of a wedgethread connection illustrating a large step of a box thread overlappinga small step of a pin thread wherein the pin and box threads havedifferent leads to prevent thread hang-up;

[0047]FIG. 14 is a vertical, sectional view of a two-step connectionconstructed with a parallel, double start thread on the small step and awedge thread on the large step; and

[0048]FIG. 15 is a vertical, sectional view of a two-step connectionconstructed with a wedge thread on the small step and a parallel, doublestart thread on the large step.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0049] FIGS. 1-3 illustrate a conventional, prior art drill pipeconnection, indicated generally at 10, in sequential stages ofdisassembly. For purposes of clarity, only the cross sectional threadprofile is illustrated in the Figures. The connection 10 is providedwith a box 12 and a pin 14 having two-step threads in the form of amating semi-dovetail, wedge helix.

[0050] A first helical pin thread tooth 16 is machined on the threadedarea 18 of a first thread step, nearest a pin end 19. A second pinthread tooth 20 is machined helically on the threaded area 22 of asecond thread step nearest an external pin shoulder 24. The thread tooth16 is a wedge thread that increases in width as it advances helicallyfrom a point nearest the pin end 19 toward the pin shoulder 24. The pinthread 20 is also a wedge thread that increases in width as it advanceshelically toward the pin shoulder 24.

[0051] The load flanks of the pin and box thread teeth are angledrelative to the central axis of the pin and box 20 to form asemi-dovetail engagement. When the connection 10 is fully made up, theload flank of the box thread tooth confines the load flank of the pinthread tooth radially. In the made up position, the wedge shaped pinthread teeth are tightly engaged within the wedge-shaped groove formedbetween the adjacent box thread teeth.

[0052] A first helical box thread tooth 26 is machined on the threadarea 28 of a first box thread step, nearest a face 30 of the box 12. Asecond box thread tooth 32 is machined helically on the threaded area 34of a second thread step extending away from the face 30. The threadteeth 26 and 32 are wedge threads that increase in width as they advancehelically away from the box face 30.

[0053] When the pin 14 and box 12 of the connection 10 are assembled asillustrated in FIG. 1, the pin thread tooth 16 is received within athread gap 36 created between adjacent helical turns of the box threadtooth 32. Simultaneously, the pin thread tooth 20 is received in athread groove 38 created between adjacent helical turns of the boxthread tooth 26.

[0054] In assembling the prior art connections illustrated in FIGS. 1-3,a centralizing stabbing guide (not illustrated) is placed over the face30 of the box 12 and the pin 14 is stabbed into the box 12 until itreaches the position illustrated in FIG. 2. At the end of the stabbingmovement, the pin thread tooth 16 on the small pin step 18 strikes thefirst box thread tooth 32 on the small box step 34. This interference ofthe threads in the pin and box prevents further axial downward movementof the pin into the box. After the pin is stabbed into the box, thestabbing guide is removed. The pin 14 is then rotated clockwise toadvance the pin thread teeth into the grooves between the box threadteeth moving the pin into the position illustrated in FIG. 1. Ascharacteristically occurs with wedge threads, the clockwise rotation isresisted as the pin thread teeth are wedged into the grooves between thebox thread teeth.

[0055] As best illustrated in FIG. 3, failure to employ a stabbing guideduring the stabbing of the two step threaded pin 14 into the box 12 canallow the pin to move eccentrically relative to the box which in turnpermits the small width pin thread teeth to hang-up in the larger groovespacings between the box thread teeth. A related, but more problematic,situation occurs when separating the pin 14 from the box 12. During thisprocess, it is necessary to employ a destabbing guide (not illustrated)to maintain coaxial alignment between the pin and box as the pin isbeing lifted out of the box to prevent the hang-up illustrated in FIG.3.

[0056] FIGS. 4-7 of the Drawings illustrate a hang-free threadedconnector of the present invention, indicated generally at 40. Theconnector 40 is provided with a semi-dovetail thread profile having thewedge helix, such as that described in the prior art of FIGS. 1-3,equipped with the thread hang-up prevention feature of the presentinvention. FIG. 4 illustrates the connection 40 fully made up with thevarious tapering width wedge thread teeth firmly lodged in the matingtapering spaces between adjacent turns of the wedge thread teeth. FIG. 5illustrates the connection 40 immediately following stabbing orimmediately preceding destabbing of the pin and box.

[0057] The connector 40 includes a pin section indicated generally at 42and a box section indicated generally at 44. The pin 42 equipped with awedge thread tooth 46 on a large step section 48 and a second threadtooth 50 on a small step section 52. Gaps or thread root openings orgrooves 47 and 49 are formed between adjacent rounds of the thread teeth46 and 50, respectively. The box 44 is equipped with a wedge threadtooth 54 formed on a large step internally threaded section 56 and asecond wedge thread tooth 58 formed on a smaller step section 60. Gaps57 and 59 are formed between the thread teeth 54 and 58, respectively.

[0058] While the present description is described with reference tothread teeth hanging up in thread gaps, it will be appreciated that eachthread tooth may be defined as the structure between adjacent threadgaps. Accordingly, thread hang-up is a possibility when the gapdimension between adjacent thread turns is greater than the structuredimension defined between succeeding gaps in the threads of the matingcomponents. Thread hang-up may occur when the radial alignment of pinand box threads is such that the pin thread tooth is smaller than thegap between adjacent box thread teeth or, when the gap between adjacentpin thread teeth is greater than the box thread tooth width.

[0059] It will be appreciated that the connection 40 is a multi-stepthreaded connection having large step sections 48 and 56 and small stepsections 52 and 60. The thread tooth 50 on the first step 52 adjacentthe free end of the pin connection 42 has a width that is greater thanthe width of the thread tooth 46 on the second step 48 further removedfrom the connection end. Similarly, the thread tooth 54 on the largestep adjacent the box end has a width that is greater than the width ofthe thread tooth 58 on the small section 60 further removed from theconnection end.

[0060] An important feature of the present invention is that any singlepin thread tooth width over the length of the small pin step 52 isgreater than any opening or groove between adjacent thread teeth in thelarge box step 56.

[0061] Thus, as illustrated in FIGS. 6 and 7, regardless of the relativeaxial positions of the pin and box, the thread tooth 50 cannot enter thegap 57 when the tooth and gap are radially aligned.

[0062] Thread hang-up between the smaller thread teeth 46 and the largerbox grooves 57 is prevented when the pin thread 50 is engaged in the boxthread 58. With the threads of the small step engaged, the pin 42 iscentralized within the box 44, preventing contact between the large stepthreads of the pin and box. When the pin and box connections are free tomove laterally relative to each other, during stabbing or destabbing,the crest or external surface of the thread tooth 50 will slide alongthe crest or external surface of the thread tooth 54 without any dangerof the two thread teeth hanging together. This feature of the presentinvention minimizes the requirement for a stabbing guide and eliminatesthe requirement for a destabbing guide.

[0063]FIG. 8 of the Drawings illustrates the hang free feature of thepresent invention indicated generally at 70, applied to a typical hookedthread with non wedging thread teeth. The connection 70 includes a boxindicated generally at 72 and a pin indicated generally at 74. A threadtooth 76, having a hook thread profile, is formed on the small step ofthe two-step pin connection 74. The thread tooth 76 has a thread width,measured axially along the connection, that is greater than a groove(root opening) 78 formed between adjacent turns of a thread tooth 82formed on the large step of the box connection. The larger width of thepin tooth 76 prevents the tooth from entering the smaller dimensions ofthe root opening 78, thereby precluding hang-up of the pin and boxthreads during the destabbing and stabbing process.

[0064]FIG. 9 illustrates a typical positive flank thread, non-wedge typeconnection, indicated generally at 90, employing the no-hang principleof the present invention. The connection 90 includes a pin indicatedgenerally at 92 and a box indicated generally at 94. A conventionalpositive flank thread tooth 96 is formed on the small step of the pinconnection 92. A similar thread tooth 98 is formed on the large step ofthe box 94. A gap 100 between adjacent turns of the thread tooth 98forms an opening that is smaller than the width of the pin tooth 96. Thepin threads 96 are thereby prevented from entering into the gap 100 topreclude hanging up of the pin and box during stabbing and destabbing.

[0065]FIG. 10 illustrates a connector of the present invention,indicated generally at 110, with a two-step thread pin 112 being stabbedor destabbed within a matching box 114. The pin thread is formed with amulti-faceted thread tooth 116 on a small step 118 of the pinconnection. A second multi-faceted thread tooth 120 is formed on alarger step 122 of the pin. The box 114 of the connection 110 isprovided with multi-faceted thread teeth 124 and 126 on the large andsmall steps, respectively, of the connection.

[0066] Adjoining turns of the box thread tooth 124 define an increasingwidth groove 130 having an axial spacing or gap that, at any pointaxially along the length of the thread, is smaller than the axial widthof the decreasing width pin tooth 116. Correspondingly, adjoining turnsof the pin thread 116 define a gap 132 that has an axial spacing smallerthan the axial width of the box tooth 124 at any place along the lengthof the tooth 124. The pin and box thread teeth form wedge threads with afull dovetail engagement.

[0067] As illustrated in FIG. 10, the dimensions of the gaps and threadteeth in the pin and box threads prevent the threads from hanging up ineach other when they contact radially. When the pin and box of theconnection 110 are made up, the engagement of the two small steps of theconnection maintains the connection exactly centered so that the smallerpin thread tooth 120 cannot engage the larger grooves 130 in the box.Once the pin is moved into the stab or destab position, the dimensionsof the opposing thread teeth and gaps between thread teeth preventhang-up of the threads.

[0068]FIG. 11 illustrates details in the construction of a conventionaltwo-step, multi-faceted, dovetail wedge thread connection, indicatedgenerally at 120. FIG. 12 illustrates a connector of the presentinvention, indicated generally at 230, constructed with a thread formsuch as that of the connection illustrated in FIG. 11, in which theteachings of the present invention have been applied to provide anon-hanging connection. The connection 230 is similar to the connectionof FIG. 10 in its made-up position.

[0069] In determining the strength of a two-step, threaded connection,it is necessary to examine the amount of metal in four critical crosssectional areas. In a typical two-step connection, there are fourdifferent threads, two on the pin and two on the box. The critical crosssectional areas are at the ends of each of these threads. On the pin,each of the two critical cross sectional areas is taken in a plane atright angles to the pin axis, through the thread root to the Internaldiameter of the connection. The critical areas for the box are taken ina similar fashion at the ends of the box threads; from the outsidediameter of the box connection through the box thread roots. The surfacearea of the material of the connection at these critical areasdetermines the strength of the connection.

[0070] Where it is desired that the connection be at least as strong asthe pipe body, i.e., a 100% connection, the thread will be cut on a pipesection having upset ends. In achieving a 100% connection, the materialin the large step pin critical cross sectional area must be greater thanthe material in the pipe body cross sectional area. The area of theconnection material in the box small step critical cross section mustalso be greater than the area of the material in the pipe body crosssection.

[0071] Similarly, in achieving a 100% connection, the combined crosssectional area of the metal in the box small step and the pin large stepmust be larger than the cross sectional area of the metal in the pipebody. In such a connection, the area of the material in the box largestep critical cross-section plus the area of the material in the pinsmall step critical cross section must be greater than the area of thematerial in the cross section of the pipe body. Ideally, the pin largestep critical cross-section, the box small step critical cross section,and the combined areas of the pin small step critical cross section andthe box large step critical cross-section should be equivalent for abalanced connection. The closer in size the box small step diameter isto the pin large step diameter, the better the connection.

[0072] The strength of a connection having the same outside diameter asof that of the pipe body, known generally as a “flush joint” connection,is also calculated in the same manner. Because of the limited amount ofmetal available for the formation of the pin and box threads, a fullopen flush joint connection is not normally capable of attaining astrength rating equal to that of the pipe body.

[0073] The previously described design considerations are illustrated asapplied to the upset connector 120 of FIG. 11. The connector 120 is aTorqueLock (TM) SIU connection for 2.875 inch pipe having a 0.217 in.radial pipe wall thickness. The connector 120 includes a pin member 132engaged in a box member 134. Multi-faceted, dovetail, wedge threads aremachined on the pipe upsets forming the pin and box portions of theconnector. The large step and small step of the connection 120 differ inradial dimension by 0.120 in. to provide a suitable stabbing anddestabbihg clearance between the pin and box threads.

[0074] The strength and efficiency of the connector 120 are determinedby evaluating the cross sectional areas of pipe material taken at fourcritical connection cross sectional areas indicated at A, B, C and Drelative to the cross sectional area of the pipe body indicated at E.For purposes of convenience, the wall thicknesses of the pipe body andconnections at the critical cross sectional areas will be used indescribing the connection. If the connection 120 is to qualify to 100%of the tension rating of the pipe body, the pin wall at A must bethicker than the pipe wall at E, the box wall at B must be thicker thanthe pipe wall at E and the combined thickness of the box wall at C plusthe pin wall at D must be greater than the thickness of the pipe wall atE. In the connection 120, the indicated components have the followingconventional dimensions, listed in TABLE 1, under the heading“CONVENTIONAL,” meeting the requirement for a joint having a connectionas strong as the pipe body: TABLE 1 CONVENTIONAL NO-HANG Outsidediameter of pipe 2.875 in. 2.875 in. body, pin end: Outside diameter ofpipe 2.875 in. 2.875 in. body, box end: Inside diameter of pin: 1.700in. 1.876 in. Outside diameter of box: 3.125 in. 3.125 in. Outsidediameter of pin: 3.125 in. 3.125 in. Pin wall thickness at A: 0.409 in.0.321 in. Box wall thickness at B: 0.418 in. 0.330 in. Box wallthickness at C: 0.203 in. 0.203 in. Pin wall thickness at D: 0.194 in.0.194 in. Pipe wall thickness at E: 0.217 in. 0.217 in. Combined pin andbox 0.7125 in. 0.6245 in. wall at A: Radial step difference: 0.120 in.0.032 in.

[0075]FIG. 12 illustrates the connector 230 of the present inventionshowing the dimensions and critical cross sectional areas at pointscorresponding to those depicted in the conventional connector 120 ofFIG. 11. The connector 230 of FIG. 12 is the connector 110 of FIG. 10illustrated in its engaged position. The various dimensions for theconnector 230 are listed in TABLE 1 under the heading “NO-HANG”.

[0076] In comparing compliance of the connector 230 with the designrequirements noted previously, it will be appreciated that the connector230 has a tension strength equal to at least 100% of that of the pipebodies being joined by the connector. Thus, the wall dimensions at A andB are greater than the pipe wall dimension at E, and the combined pipewall dimensions at C and D are greater than the wall dimension at E.

[0077] TABLE 1 also reveals that the connector 230 has a combinedconnector wall thickness that is less than that of the conventionalconnector 120 of FIG. 11. The combined wall section of the connector 230contributes to the flexibility of the connector and reduces theincidence of fatigue failure. The connector 230 also has a greatercentral opening than the conventional connector 120 of FIG. 11. As aresult, the connector 230 provides a reduction in the restriction tofluid flow and increases the central opening for improved entry ofequipment and tools. All these features are realized in the connector ofthe present invention, with the included benefit of a no-hang capabilityduring stabbing and destabbing of the connection.

[0078]FIG. 13, illustrates a modified form of a two-step dovetail wedgeconnection of the present invention, indicated generally at 200. Theconnection 200, illustrated in broken away cross sectional detail,depicts a small step pin tooth 202 and a large step box tooth 204. Thelarge thread step of the box is indicated at 210 and the small threadstep of the pin is indicated at 215.

[0079] The average lead of the box thread 204 is indicated as thedimension A. The average lead of the small step pin thread is shown asthe dimension B. The lead between the load flanks of the box thread 204is illustrated as the dimension C and the lead between the box threadstab flanks is illustrated as the dimension D. The dimension E depictsthe load flank lead of the pin thread 202 and the dimension F depictsthe stab flank lead of the pin thread. It is noted that, even though thetooth width of the pin thread is changing along the axial development ofthe thread, the average lead between adjacent thread turns remainsunchanged. Similarly, the average lead of the changing width pin threadremains the same throughout its axial development. Since the averagelead of the box thread is the same as the average lead of the pinthread, the pin and box components advance axially at the same rate asthey are being threaded together.

[0080] As indicated in FIG. 13, the load flank lead of the pin thread isgreater than the load flank lead of the box thread and the stab flanklead of the box thread is greater than the stab flank lead of the pinthread. The resulting differences in the dimensions and positions of thepin and box threads during stabbing and destabbing prevent the pinthread tooth 202 from entering the gap 220 between adjacent turns of thebox thread tooth 204. The interference between the thread crestsprevents the pin thread from entering the gap 220 except for the finalturn of the pin thread adjacent the pin end.

[0081]FIG. 14 of the drawings illustrates a form of the Invention,indicated generally at 300, in which hang up is prevented by providingdifferent type threads on the small step and large step of theconnection. A pin 310 is provided with a large thread step having awedge thread tooth 312 extending helically along the external pinsurface. Dual start, parallel thread teeth 314 and 316 extend helicallyover the external surface of a small step of the pin 310. The dual startthread teeth 314 and 316 begin adjacent a pin nose 318 and progresshelically toward the large step of the pin, side-by-side, over thelength of the small pin step. The thread tooth 314 begins adjacent thepin nose 318 and the thread tooth 316 begins one thread width away fromthe pin nose.

[0082] A Two-step box 320, designed to engage and threadedly connect tothe pin 310, is provided with wedge threads 322 on the large step andparallel, dual start threads 324 and 326 on the box small step. FIG. 14illustrates the connection 300 during the process of stabbing ordestabbing the pin 310 into or out of the box 320.

[0083] During the stabbing or destabbing process of the connection 300,the crests of the dual start threads 314 and 316 span the gaps formedbetween the thread crests of adjacent turns of the box wedge threadtooth 322. Accordingly, any lateral displacement of the pin relative tothe box during the stabbing and destabbing process engages the crests ofthe small pin thread teeth against the crest of the large box threadtooth to prevent hang-up.

[0084]FIG. 15 illustrates a modified form of the Invention, indicatedgenerally at 400, in which dissimilar threads are placed on the smalland large steps of a multi-step connection to prevent hang-up of theconnection during stabbing and destabbing. The connection is comprisedof a two-step threaded pin 410 designed to mate with a correspondinglythreaded box 411. The pin 410 is provided with a small step threadedarea having a wedge thread tooth 412 extending helically over theexternal surface of the small step. Dual start, parallel thread teeth414 and 416 are provided over the pin large step. The box 411 isprovided with a helical thread tooth 418 extending over the box smallstep. Dual start, parallel thread teeth 420 and 422 extend over theinternal surface of the box large step.

[0085] During stabbing and destabbing of the connection 400, the crestsof the thread teeth 420 and 422 span the gap between crests of adjacentrevolutions of the pin wedge thread tooth 412 to prevent hang-up.

[0086] The design and use of the Illustrated embodiments of the presentinvention have been set forth in detail in order that the invention maybe clearly understood as it may be employed in applications andcircumstances different from those anticipated in the preferredsettings. The specific embodiments of the invention described herein aremerely illustrative of the many and diverse forms that this inventionmay take, and of the many and diverse applications that this inventionmay have throughout industry in general. Accordingly, the foregoingdescription is not to be considered as limiting to the particularembodiments that have been illustrated and described. Rather, thisinvention is intended to be regarded broadly within the scope of theappropriate interpretation of the following Claims.

1. A multi-step threaded connector, comprising: a pin connection havinga large diameter pin thread area and a smaller diameter pin thread areaformed about a central pin axis, a box connection with a large diameterbox thread area and a smaller diameter box thread area formed about acentral box axis, said large diameter pin thread area being threadedlyreceivable within said large diameter box thread area and said smallerdiameter pin thread area being threadedly receivable within said smallerdiameter box thread area, a pin thread tooth coaxially formed externallyon said smaller diameter pin thread area, said pin thread toothadvancing helically from one axial point on said pin connection toward anearest axial end of said pin connection, a pin crest on said pin threadtooth, said pin crest having a crest width measured parallel to said pinaxis, a box thread tooth coaxially formed internally on said largediameter box thread area, said box thread tooth advancing helically fromone axial point on said box connection toward a nearest axial end ofsaid box connection, and a box thread groove defined between adjacenthelical segments of said box thread tooth, said box thread groove havinga groove width measured parallel to said box axis that is smaller thansaid pin crest width whereby said pin tooth cannot radially enter saidbox thread groove sufficiently to hang-up said pin and box upon stabbingor destabbing of said pin.
 2. A multi-step thread connector as definedin claim 1 wherein the width of said pin thread tooth increases alongthe helical thread development in a direction away from said axial endof said pin.
 3. A multi-step thread connector as defined in claim 1wherein pin and box thread teeth of said connector are adapted to engagein a wedge-thread.
 4. A multi-step thread connector as defined in claim1 wherein pin and box thread teeth of said connector are adapted toengage in a hook thread.
 5. A multi-step thread connector as defined inclaim 1 wherein pin and box thread teeth of said connector have crosssectional profiles with at least one thread flank of each thread beingparallel with a thread flank of the other.
 6. A multi-step threadconnector as defined in claim 1 wherein pin and box thread teeth of saidconnector are adapted to threadedly engage with each other in a dovetailconnection.
 7. A multi-step thread connector as defined in claim 6wherein pin and box thread teeth of said connector are adapted to engagein a wedge-thread.
 8. A multi-step threaded pin connection having firstand second threaded areas, said first threaded area having a smallerdiameter than said second threaded area, comprising: a first threadtooth extending helically over said first threaded area, a second threadtooth extending helically over said second threaded area, said firsttooth having a first tooth crest positioned between a stab flank and aload flank of said first tooth, and said second tooth having a secondtooth crest positioned between a stab flank and a load flank of saidsecond tooth, said second tooth crest being larger than said first toothcrest.
 9. A multi-step thread as defined in claim 8 wherein said pinthread tooth has a width that increases along the helical threaddevelopment in a direction away from a nearest axial end of said pin.10. A multi-step thread connector as defined in claim 8 furthercomprising pin and box thread teeth that are adapted to threadedlyengage with each other in a wedge-thread.
 11. A multi-step threadconnector as defined in claim 8 further comprising pin and box threadteeth that are adapted to engage with each other in a hook thread.
 12. Amulti-step thread connector as defined in claim 8 wherein said pin andbox thread teeth have cross sectional profiles with at least one threadflank of each thread being parallel with a thread flank of the other.13. A multi-step thread connector as defined in claim 8 furthercomprising pin and box thread teeth that are adapted to threadedlyengage with each other in a dovetail connection.
 14. A multi-step threadconnector as defined in claim 13 further comprising pin and box threadteeth that are adapted to engage with each other in a wedge-thread. 15.A multi-step threaded box connection having first and second threadedareas, said first threaded area having a larger diameter than saidsecond threaded area, comprising: a first thread tooth formed helicallyover said first threaded area defining a first thread groove betweenadjacent helical sections of said first thread tooth, and a secondthread tooth formed helically over said second threaded area defining asecond thread groove between adjacent helical sections of said secondthread tooth, said second thread groove being wider than said firstthread groove.
 16. A multi-step threaded box connection as defined inclaim 15 wherein said first thread tooth has a width that decreasesalong the helical thread development in a direction away from a nearestaxial end of said box.
 17. A multi-step threaded box connection asdefined in claim 15 wherein said box thread tooth comprises awedge-thread.
 18. A multi-step threaded box connection as defined inclaim 15 wherein said box thread tooth comprises a hook thread.
 19. Amulti-step threaded box connection as defined in claim 15 wherein saidbox thread tooth has a cross sectional profile with parallel threadflanks.
 20. A multi-step threaded box connection as defined in claim 15wherein said box thread tooth has a dovetail cross sectional threadprofile.
 21. A multi-step threaded box connection as defined in claim 20wherein said box thread tooth comprises a wedge-thread.
 22. A multi-stepthreaded box connection as defined in claim 15, further comprising: acentral axis in said connection with said first and second thread teethextending helically and axially along an inner surface of said boxconnection, said box teeth defining box thread grooves between adjacenthelical sections of said thread teeth, said box thread grooves havingwidths that decrease in width in a direction away from a nearest axialend of said box connection.
 23. A multi-step threaded connection asdefined in claim 22 further including a pin connection having a pinthread tooth with a width that increases along a helical threaddevelopment in a direction away from a nearest axial end of said pin.24. A multi-step threaded connection as defined in claim 22 furthercomprising pin and box thread teeth adapted to engage and form awedge-thread.
 25. A multi-step threaded connection as defined in claim22 further comprising pin and box thread teeth adapted to engage andform a hook thread.
 26. A multi-step threaded connection as defined inclaim 22 wherein said pin and box thread teeth have cross sectionalprofiles with at least one thread flank of each thread tooth beingparallel with a thread flank of the other thread tooth.
 27. A multi-stepthreaded connection as defined in claim 22 further comprising pin andbox thread teeth adapted to threadedly engage with each other in adovetail connection.
 28. A multi-step threaded connection as defined inclaim 27 further comprising pin and box thread teeth adapted to engagewith each other to form a wedge-thread.
 29. A threaded connection havinga pin and box adapted to be threadedly engaged with and disengaged fromeach other, comprising: a threaded pin having a helically extending pinthread tooth extending from a pin base area toward a pin end area in thevicinity of a near axial end of the pin, said pin thread tooth having across sectional area defined in part by a pin thread load flank, a pinthread stab flank and a pin thread crest extending between the pinthread load flank and the pin thread stab flank, a threaded box having ahelically extending box thread tooth extending from a box base areatoward a box end area in the vicinity of a near axial end of the box,said box thread tooth having a box thread crest defining a thread rootentry space between adjacent box thread crests in helical sections ofsaid box thread tooth, and said pin thread crest having a widthdimension, measured axially along said pin, that is greater than a widthdimension of an adjacent box thread root entry space, measured axiallyalong said box, when said pin is received in said box with said pin andbox threads threadedly disengaged from each other.
 30. A threadedconnection as defined in claim 29 wherein said pin thread tooth has awidth that increases along the helical thread development in a directionaway from a nearest axial end of said pin.
 31. A threaded connection asdefined in claim 29 further comprising pin and box threads having crosssectional thread forms in the configurations of V, tapered, square,round, dovetail, wedge, chevron, semi-dovetail, multifaceted and/orcombinations of such configurations.
 32. A threaded connection asdefined in claim 31 further comprising pin and box thread teeth adaptedto engage and form a hook thread.
 33. A threaded connection as definedin claim 31 wherein said pin and box thread teeth have cross sectionalprofiles with at least one thread flank of each thread tooth beingparallel with a thread flank of the thread tooth.
 34. A threadedconnection as defined in claim 31 further comprising pin and box threadteeth adapted to threadedly engage each other in a dovetail connection.35. A threaded connector as defined in claim 34 further comprising pinand box thread teeth adapted to engage in a wedge-thread connection. 36.A threaded connection having a pin receivable within a box and adaptedto be threadedly engaged and disengaged to selectively secure tubularmembers together, comprising: an axially extending pin connection havinga helical pin thread crest at a radially outer point on a pin threadtooth, said pin thread crest having a crest width, a helical box threadtooth defining a helical box thread groove between adjacent turns ofsaid box thread tooth, said box thread groove having a groove width, andsaid pin thread crest being wider than said box groove width in adjacentpin and box threads at all positions where the pin and box threads aredisengaged and the pin is at least partially received in the box.
 37. Athreaded connection as defined in claim 36 wherein said pin thread toothhas a width that increases along the helical thread development in adirection away from a nearest axial end of said pin.
 38. A threadedconnection as defined in claim 36 further comprising pin and box threadteeth adapted to engage and form a wedge-thread.
 39. A threadedconnection as defined in claim 36 further comprising pin and box threadteeth adapted to engage and form a hook thread.
 40. A threadedconnection as defined in claim 36 wherein said pin and box thread teethhave cross sectional profiles with at least one thread flank of eachthread being parallel with a thread flank of the other.
 41. A threadedconnection as defined in claim 36 further comprising pin and box threadteeth adapted to threadedly engage each other in a dovetail connection.42. A threaded connector as defined in claim 41 further comprising pinand box thread teeth adapted to engage in a wedge-thread.
 43. Multiplecrested pin thread teeth extending helically around an axially extendingtubular body from a base point on said tubular body toward a terminationpoint in the vicinity of a nearest axial end on said tubular bodywherein a crested pin thread tooth of one of said thread teeth has awider crest in an area adjacent said termination point than a crest ofanother of said thread teeth in an area adjacent said base point.
 44. Amethod of manufacturing a threaded pin and box connector, comprising:forming a helically extending pin thread tooth on a pin of saidconnector, forming a pin thread crest on said pin thread tooth, forminga helically extending box thread tooth on a box of said connector,forming a box thread groove between adjacent turns of said box threadtooth, and forming said pin thread crest with a width greater than thewidth of said box thread groove on substantially all pin thread teeththat may be received within said box without also being threadedlyengaged in said box.
 45. A multi-step threaded connector, comprising: apin connection having a large diameter pin thread area and a smallerdiameter pin thread area formed about a central pin axis, a boxconnection with a large diameter box thread area and a smaller diameterbox thread area formed about a central box axis, said large diameter pinthread area being threadedly receivable within said large diameter boxthread area and said smaller diameter pin thread area being threadedlyreceivable within said smaller diameter box thread area, a pin threadtooth coaxially formed externally on said smaller diameter pin threadarea, said pin thread tooth advancing helically from one axial point onsaid pin connection toward a nearest axial end of said pin connection, apin crest on said pin thread tooth, said pin crest having a crest widthmeasured parallel to said pin axis, a box thread tooth coaxially formedinternally on said large diameter box thread area, said box thread toothadvancing helically from one axial point on said box connection toward anearest axial end of said box connection, and wherein the lead of saidbox thread tooth is different from the lead of said pin thread tooth inareas in which said box thread tooth overlaps said pin thread toothduring stabbing and destabbing of said pin and box.
 46. A multi-stepthread connector as defined in claim 45 wherein the width of said pinthread tooth increases along the helical thread development in adirection away from said axial end of said pin.
 47. A multi-step threadconnector as defined in claim 45 further comprising pin and box threadteeth adapted to engage in a wedge-thread.
 48. A multi-step threadconnector as defined in claim 45 further comprising pin and box threadteeth adapted to engage in a hook thread.
 49. A multi-step threadconnector as defined in claim 45 wherein said pin and box thread teethhave cross sectional profiles with at least one thread flank of eachthread being parallel with a thread flank of the other.
 50. A multi-stepthread connector as defined in claim 45 further comprising pin and boxthread teeth adapted to threadedly engage with each other in a dovetailconnection.
 51. A multi-step thread connector as defined in claim 50further comprising pin and box thread teeth adapted to engage in adovetail wedge-thread.
 52. A multi-step thread connector as defined inclaim 45 wherein the average lead of a pin thread tooth is equal to theaverage lead of a box thread tooth.
 53. A multi-step thread connector asdefined in claim 52 wherein the lead between box thread tooth loadflanks is a dimension “C”, the lead between box thread tooth stab flanksis a dimension “D”, the lead between pin thread tooth load flanks is adimension “E”, the lead between pin thread tooth stab flanks is adimension “F”, and wherein C is less than E and D is greater than F. 54.A multi-step thread connector as defined in claim 51 wherein the leadbetween box thread tooth load flanks is a dimension “C”, the leadbetween box thread tooth stab flanks is a dimension “D”, the leadbetween pin thread tooth load flanks is a dimension “E”, the leadbetween pin thread tooth stab flanks is a dimension “F”, and wherein Cis less than E and D is greater than F.
 55. A multi-step threadconnector, comprising: a pin connection having a large diameter pinthread area and a smaller diameter pin thread -area formed about acentral pin axis, a box connection with a large diameter box thread areaand a smaller diameter box thread area formed about a central box axis,said large diameter pin thread area being threadedly receivable withinsaid large diameter box thread area and said smaller diameter pin threadarea being threadedly receivable within said smaller diameter box threadarea, a pin thread tooth coaxially formed externally on said smallerdiameter pin thread area, said pin thread tooth advancing helically fromone axial point on said pin connection toward a nearest axial end ofsaid pin connection, a pin crest on said pin thread tooth, said pincrest having a crest width measured parallel to said pin axis, a boxthread tooth coaxially formed internally on said large diameter boxthread area, said box thread tooth advancing helically from one axialpoint on said box connection toward a nearest axial end of said boxconnection, and said pin thread tooth on said smaller diameter pin areahaving a cross sectional profile different from the cross sectionalprofile of said box thread tooth on said larger diameter box thread areawhereby a pin thread tooth cannot hang-up in the spacing betweenadjacent turns of a box thread tooth.
 56. A multi-step thread connectoras defined in claim 55 wherein said smaller diameter pin thread areaincludes a pin thread tooth having a wedge thread profile and saidlarger diameter box thread area includes a box thread tooth having aparallel thread profile.
 57. A multi-step thread connector as defined inclaim 55 wherein said smaller diameter pin thread area includes a pinthread tooth having a parallel thread profile and said larger diameterbox thread area includes a box thread tooth having a wedge threadprofile.
 58. A multi-step thread as defined in claim 56 furthercomprising dual start, parallel thread teeth on said larger diameter boxthread area.
 59. A multi-step thread as defined in claim 57 furthercomprising dual start, parallel thread teeth on said smaller diameterpin thread area.